Hydrothermally stable metal promoted zeolite beta for NOx reduction

ABSTRACT

The present invention is directed to a metal-promoted zeolite beta catalyst useful in the selective catalytic reduction of nitrogen oxides with ammonia in which the zeolite beta is pre-treated so as to provide the zeolite with improved hydrothermal stability.  
     The stabilized beta zeolite is provided by incorporating into the zeolite structure non-framework aluminum oxide chains. The aluminum oxide chains can be incorporated into the zeolite structure by a unique steaming regimen or by treatment with rare earth metals, such as cerium. The treatment process is unlike well-known methods of dealuminizing zeolites for the purpose of increasing the silica to alumina ratio. In the present invention, the non-framework aluminum oxide is characterized by FT-IR by a peak at 3781±2 cm −1 , which when present, stabilizes the zeolite against further dealumination such as under oxidizing and harsh hydrothermal conditions.

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] The present invention is concerned with a method of catalyzingthe reduction of nitrogen oxides with ammonia, especially the selectivereduction of nitrogen oxides, with ammonia in the presence of oxygen,using zeolite catalysts, especially metal-promoted zeolite catalysts.The invention is also directed to hydrothermally stable zeolitecatalysts and methods of making same.

[0003] 2. The Related Art

[0004] Both synthetic and natural zeolites and their use in promotingcertain reactions, including the selective reduction of nitrogen oxideswith ammonia in the presence of oxygen, are well known in the art.Zeolites are aluminosilicate crystalline materials having rather uniformpore sizes which, depending upon the type of zeolite and the type andamount of cations included in the zeolite lattice, range from about 3 to10 Angstroms in diameter.

[0005] Japanese Patent Publication (Kokai) No. 51-69476, published Jun.16, 1976 on Application No. 49-142463, filed Dec. 13, 1974, discloses amethod for reducing nitrogen oxides in waste gases by reaction withammonia in the presence of a metal-promoted, dealuminized synthetic ornatural mordenite zeolite. The resistance of the catalyst to sulfurouspoisons, particularly sulfur trioxide and sulfuric acid mist, is said tobe enhanced by dealuminizing the mordenite to increase the silica toalumina ratio to more than 12, preferably to more than 15. The zeoliteis promoted with 0.5 to 30 wt. % of at least one of a number ofpromoters including copper, vanadium, chromium, iron, cobalt or nickeland used at a reaction temperature of 200° C. to 500° C. with from 0.5to three times the stiochiometric amount of ammonia reductant. Example 1of the Publication illustrates an iron-promoted mordenite ore as beingeffective for the reduction of nitrogen oxides. In connection withExample 2, it is stated that a slight decrease of the activity of a highsilica to alumina ratio, copper-promoted mordenite catalyst isrecognized when sulfur trioxide is included in the gas stream. However,an “extreme improvement” of resistance to sulfur trioxide poisoning isnoted in comparison with a copper mordenite which has not beendealuminized to increase the silica to alumina ratio.

[0006] UK Patent Application No. 2,193,655A discloses a catalystcontaining a low surface area titania and a copper-promoted zeolite foruse in the reduction of nitrogen oxides with ammonia. The zeolite has anaverage pore diameter of 10 Angstroms or less, preferably 8 Angstroms orless, and a silica to alumina molar ratio of 10 or more, preferably 20or more; the resultant titania/-promoted zeolite catalysts having thesecharacteristics are stated to have good mechanical strength and to beresistant to volatile catalyst poisons such as arsenic, selenium,tellurium, etc., contained in exhaust gases. Examples of suitablezeolites are mordenite, ZSM-5, and ferrierite.

[0007] U.S. Pat. No. 4,297,328 discloses a “three-way conversion”catalytic process for the simultaneous catalytic oxidation of carbonmonoxide and hydrocarbons and reduction of nitrogen oxides for purifyingthe exhaust gas of automobile engines operated within a prescribed rangeof air to fuel ratio (column 4, lines 63-68). The disclosed catalyst isa copper-promoted zeolite having a silica to alumina ratio greater than10, preferably greater than 20 (column 6, lines 23-28). Representativehigh-silica zeolites are described at columns 6-8 of the patent andinclude (column 6, lines 29-33) silicalite (as described in U.S. Pat.No. 4,061,724), ZSM-8, ZSM-11, ZSM-12, hyper Y, ultrastabilized Y, Beta,mordenite and erionite. Ultrastabilized Y is described (column 7, lines22-25) as “a form of zeolite Y which has been treated to give it theorganophilic characteristic of the adsorbents of the present invention.”Example 6 of the patent is stated to show no measurable loss incombustion activity of the copper-prompted zeolite catalyst due tosulfur poisoning (exposure of the catalyst to methylmercaptan in thegaseous stream). The patent thus discloses the utility of thecopper-promoted specified zeolites for three-way conversion in anexhaust gas generated by a lean air to fuel ratio-combustion mixture.

[0008] The art thus shows an awareness of the utility of metal-promotedzeolite catalysts including, among others, iron-promoted andcopper-promoted zeolite catalysts, for the selective catalytic reductionof nitrogen oxides with ammonia.

[0009] In accordance with U.S. Pat. No. 4,961917, there is provided animproved method for the reduction of nitrogen oxides with ammonia. Themethod described in this commonly assigned U.S. patent comprising thefollowing steps. A gaseous stream containing nitrogen oxides andammonia, and which may also contain oxygen, is contacted at atemperature of from about 250° C. to 600° C. with a sulfur-tolerantcatalyst composition. The catalyst composition comprises a zeolitehaving a silica to alumina ratio of at least about 10, and a porestructure which is interconnected in all three crystallographicdimensions by pores having an average kinetic pore diameter of at leastabout 7 Angstroms, e.g. from about 7 to 8 Angstroms, and one or both ofan iron and a copper promoter present in the zeolite, for example, inthe amount of from about 0.1 to 30 percent by weight, preferably fromabout 1 to 5 percent by weight, of the total weight of promoter pluszeolite. The zeolite comprises one or more of USY, Beta and ZSM-20. Arefractory binder may be admixed with the zeolites. An iron-promotedzeolite beta is preferred and has been commercialized for removingNO_(x) by selective catalytic reduction such as from gas turbineexhaust.

[0010] The iron-promoted zeolite beta has been an effective catalyst forthe selective reduction of nitrogen oxides such as by the reduction ofnitrogen oxides with ammonia. Unfortunately, it has been found thatunder harsh hydrothermal conditions, such as reduction of NO_(x) fromgas turbine exhaust at temperatures exceeding 500° C., the activity ofthe iron-promoted zeolite beta begins to decline. This decline inactivity is believed to be due to destabilization of the zeolite such asby dealumination and consequent reduction of metal-containing catalyticsites within the zeolite. To maintain the overall activity of NO_(x)reduction, increased levels of the iron-promoted zeolite catalyst mustbe provided. As the levels of the zeolite catalyst increase so as toprovide adequate NO_(x) removal, there is an obvious reduction in thecost efficiency of the process for NO_(x) removal as the costs of thecatalyst rise.

[0011] Accordingly, there is a need to improve the process for theselective catalytic reduction of NO_(x) by ammonia so as to maintaincatalytic activity, even under harsh hydrothermal conditions.

[0012] There is a further general need for improving the hydrothermalstability of aluminosilicate zeolite catalysts, especiallymetal-promoted zeolites so as to stabilize such materials fromdealumination and loss of catalytic sites during use.

SUMMARY OF THE INVENTION

[0013] In accordance with the present invention, a metal-promotedzeolite catalyst useful in the selective catalytic reduction of nitrogenoxides with ammonia is pre-treated so as to provide the zeolite withimproved hydrothermal stability. The improved stability is believed tomanifest in an improved resistance to dealumination and consequentresistance to removal of catalytic sites from within the zeolite.

[0014] In another aspect of the invention, aluminosilicate zeolitecatalysts, in general, are stabilized such as against hydrothermalconditions by treating the aluminosilicate zeolites in a mannerheretofore not known in the prior art.

[0015] Still further, the present invention is directed to a stablealuminosilicate zeolite as well as a metal-promoted aluminosilicatezeolite which is stabilized against loss of catalytic sites.

[0016] The stabilized aluminosilicate zeolites in accordance with thisinvention are provided by incorporating into the zeolite structurenon-framework aluminum oxide chains, which are believed to be associatedwith or even linked to the aluminosilicate framework of the zeolite. Thepresence of the non-framework aluminum oxide chains is manifest by aunique peak found in the FT-IR spectrum. The presence of this peak at3781±2 cm⁻¹ is associated with the improved stability of the zeolite.The non-framework aluminum oxide chains can be incorporated into thezeolite structure by several processes known at this time, including viaa unique steaming regimen or by treatment with rare earth metals, suchas cerium. While not wishing to be bound by any theory, it is believedthat the treatment of the aluminosilicate zeolite decouples aluminumoxide temporarily from the zeolitic framework. The decoupled aluminumoxide molecules are then recombined and linked as a chain, which isreattached to or otherwise associated with the zeolite framework. Thetreatment process is unlike well-known methods of dealuminizing zeolitesfor the purpose of increasing the silica to alumina ratio. In thepresent invention, the alumina is not removed from the zeolite but isbelieved to be rearranged and otherwise attached or associated with thealuminosilicate framework. The non-framework aluminum oxide chainsassociated with the FT-IR absorption peak at 3781±2 cm⁻¹ appear tostabilize the zeolite against further dealumination such as underoxidizing and harsh hydrothermal conditions.

[0017] The aluminosilicate zeolites which can be stabilized inaccordance with this invention are not known to be limited. Thosezeolites which have known catalytic activity, in particular, medium tolarge pore zeolites appear to be most usefully treated. In general,zeolites having an average pore diameter of at least about 5 Δ arebelieved to be effectively treated in accordance with this invention.Catalytic processes which involve oxidizing and/or hydrothermalconditions can be operated very effectively with the stabilizedaluminosilicate zeolites, including metal-promoted aluminosilicatezeolites treated in accordance with this invention. More specifically,it has been found that iron-promoted zeolite beta which has been treatedto provide the non-framework aluminum oxide chains associated with thezeolite framework has increased hydrothermal stability than the ironpromoted zeolite beta catalyst which has not been so treated. Aniron-promoted zeolite beta catalyst treated in accordance with thisinvention yields improved activity in the selective catalytic reductionof NO, with ammonia, especially when operated under high temperatures ofat least about 500° C. is and high water vapor environments of 10% ormore.

BRIEF DESCRIPTION OF THE DRAWINGS

[0018]FIG. 1 is a schematic of the aging of the stabilized zeolite ofthis invention.

[0019]FIG. 2 is a FT-IR Spectra of a stabilized zeolite beta of thisinvention and a standard zeolite beta.

[0020]FIG. 3 is a plot of activity for NOx conversion at 430° C.comparing the activity of stabilized zeolite beta catalysts inaccordance with the present invention and a non-treated zeolite betacatalyst.

[0021]FIG. 4 is a plot of activity for NOx conversion at 550° C.comparing the activity of stabilized zeolite beta catalysts inaccordance with the present invention and a non-treated zeolite betacatalyst.

DETAILED DESCRIPTION OF THE INVENTION

[0022] In order to reduce the emissions of nitrogen oxides from flue andexhaust gases, such as the exhaust generated by gas turbine engines,ammonia is added to the gaseous stream containing the nitrogen oxidesand the gaseous stream is then contacted with a suitable catalyst atelevated temperatures in order to catalyze the reduction of nitrogenoxides with ammonia. Such gaseous streams often inherently containsubstantial amounts of oxygen. For example, a typical exhaust gas of aturbine engine contains from about 2 to 15 volume percent oxygen andfrom about 20 to 500 volume parts per million nitrogen oxides, thelatter normally comprising a mixture of NO and NO₂. Usually, there issufficient oxygen present in the gaseous stream to oxidize residualammonia, even when an excess over the stoichiometric amount of ammoniarequired to reduce all the nitrogen oxides present is employed. However,in cases where a very large excess over the stoichiometric amount ofammonia is utilized, or wherein the gaseous stream to be treated islacking or low in oxygen content, an oxygen-containing gas, usually air,may be introduced between the first catalyst zone and the secondcatalyst zone, in order to insure that adequate oxygen is present in thesecond catalyst zone for the oxidation of residual or excess ammonia.The reduction of nitrogen oxides with ammonia to form nitrogen and H₂Ocan be catalyzed by metal-promoted zeolites to take place preferentiallyto the oxidation of ammonia by the oxygen, hence the process is oftenreferred to as the “selective” catalytic reduction (“SCR”) of nitrogenoxides, and is sometimes referred to herein simply as the “SCR” process.

[0023] The catalysts employed in the SCR process ideally should be ableto retain good catalytic activity under high temperature conditions ofuse, for example, 400° C. or higher, under hydrothermal conditions andin the presence of sulfur compounds. High temperature and hydrothermalconditions are often encountered in practice, such as in the treatmentof gas turbine engine exhausts. The presence of sulfur or sulfurcompounds is often encountered in treating the exhaust gases ofcoal-fired power plants and of turbines or other engines fueled withsulfur-containing fuels such as fuel oils and the like.

[0024] Theoretically, it would be desirable in the SCR process toprovide ammonia in excess of the stoichiometric amount required to reactcompletely with the nitrogen oxides present, both to favor driving thereaction to completion and to help overcome adequate mixing of theammonia in the gaseous stream. However, in practice, significant excessammonia over the stoichiometric amount is normally not provided becausethe discharge of unreacted ammonia from the catalyst would itselfengender an air pollution problem. Such discharge of unreacted ammoniacan occur even in cases where ammonia is present only in astoichiometric or sub-stoichiometric amount, as a result of incompletereaction and/or poor mixing of the ammonia in the gaseous stream.Channels of high ammonia concentration are formed in the gaseous streamby poor mixing and are of particular concern when utilizing catalystscomprising monolithic honeycomb-type carriers comprising refractorybodies having a plurality of fine, parallel gas flow paths extendingtherethrough because, unlike the case with beds of particulatecatalysts, there is no opportunity for gas mixing between channels. Itis, therefore, also desirable that the catalyst employed to catalyze theselective catalytic reduction of nitrogen oxides, be effective tocatalyze the reaction of oxygen and ammonia, in order to oxidize excessor unreacted ammonia to N₂ and H₂O.

[0025] Commonly assigned U.S. Pat. No. 4,961,917 is predicated on thediscovery that a certain class of zeolites, especially when promotedwith a promoter such as iron or copper, especially iron, exhibitsdesired characteristics as described above by providing a sulfurtolerant catalyst which shows good activity for both (1) the selectivecatalytic reduction of nitrogen oxides by reaction with ammonia, even inthe presence of oxygen, and (2) the oxidation of ammonia with oxygenwhen nitrogen oxides are at very low concentrations. The catalystsdisclosed in the above referenced patent retain such activity even afterprolonged exposure to high temperatures, hydrothermal conditions, andsulfate contamination of the type often encountered in use, e.g., in thetreatment of coal-fired-power plants or turbine engine exhaust gases.

[0026] Generally, in accordance with the practices of the presentinvention and as disclosed in U.S. Pat. No. 4,961,917, a catalyst isprovided which comprises a zeolite having specific properties asdescribed below, and which is promoted by a metal, preferably iron, inorder to enhance its catalytic activity. The zeolite may be provided inthe form of a fine powder which is admixed with or coated by a suitablerefractory binder, such as bentonite or silica, and formed into a slurrywhich is deposited upon a suitable refractory carrier. Typically, thecarrier comprises a member, often referred to as a “honeycomb” carrier,comprising one or more refractory bodies having a plurality of fine,parallel gas flow passages extending therethrough. Such carriers are, ofcourse, well known in the art and may be made of any suitable materialsuch as cordierite or the like. The catalysts of the present inventionmay also be provided in the form of extrudates, pellets, tablets orparticles of any other suitable shape, for use as a packed bed ofparticulate catalyst, or as shaped pieces such as plates, saddles,tubes, or the like.

[0027] Useful catalysts show a marked resistance to poisoning bysulfates (or other sulfur compounds) which are often contained in thegas streams which are treatable by the catalysts of the presentinvention. Without wishing to be bound by any particular theory, itappears that SO₂ poisoning has both short term and long term effects.For example, flowing a gas stream containing 2,000 parts per million byvolume (“Vppm”) SO₂ through catalysts comprising copper-promoted smallto medium pore zeolites such as ZSM-5, naturally occurring chabazite andclinoptilolite, resulted in 10 to 40 percent reduction in SCR processactivity. Even at SO₂ levels as low as 130 Vppm SO₂, significantactivity reduction for the SCR process was noted for such catalysts. Onthe other hand, larger pore zeolites such as Y, L and USY exhibited noshort-term SO₂ susceptibility. With operating temperatures at about 350°C., the short-term SO₂ poisoning effect on a copper-promoting mordenitewas shown to be reversible. Thus, when the supply of SO₂ to the test gasstream passing through the copper-promoted mordenite catalyst was turnedoff, the activity for catalytic reduction of NO immediately returned tothe same level attained by the catalyst prior to introducing the SO₂.Apparently, SO₂ is absorbed, but not tightly bound in the zeolite pores.In the case of the small to medium pore zeolites, this competitionabsorption with NH₃ and NO probably results in a physical blockageand/or diffusional restriction.

[0028] On the other hand, when zeolite catalysts are subjected to higherSO₂ concentrations for longer periods of time, such as 5,000 Vppm SO₂for protracted periods, such as overnight, a 15 to 25 percent activityreduction for the SCR process was noted for copper-promoted, syntheticiron-free zeolites. A 60 percent reduction in SCR process activity istypical for Fe₂O₃ containing natural chabazite. Similar results weresustained with iron-promoted mordenite catalysts.

[0029] Even-at lower levels of SO₂ concentration, similar to thoselikely to be encountered in commercial operations, a permanent activityloss for the SCR process is shown by many is zeolite catalysts. Forexample, a copper-promoted mordenite catalyst was subjected overnight topassage through it of a gaseous stream containing 540 Vppm SO₂, andshowed a permanent activity loss comparable to that described above forthe catalysts subjected to the 5,000 Vppm SO₂-containing gas.

[0030] For zeolites with silica-alumina ratios of less than 8, theactivity loss appears to be associated with insufficient stability underthe simulated acidic aging conditions. As indicated by the prior artnoted above, the utilization of high ratios of silica to alumina isknown to enhance acid resistance of the zeolite and to provide enhancedresistance of the zeolite to acid sulfur poisoning. Generally, silica toalumina ratios well in excess of the minimum of 8 may be employed.Conversion efficiencies of 90 to 93% for NO_(x) reduction with ammoniahave been attained with fresh copper-promoted Beta zeolites havingsilica to alumina ratios of 20, 26, 28, 37 and 62. A conversionefficiency of 77% was attained by a fresh copper-promoted ZSM-5 zeolitehaving a silica to alumina ratio of 46. However, fresh copper-promotedUSY zeolites with silica to alumina ratios of, respectively, 8 and 30provided 85% and 39% conversions of NO_(x) suggesting that at least USY,silica to alumina ratios should be significantly less than 30.

[0031] However, resistance to short term sulfur poisoning and theability to sustain a high level of activity for both the SCR process andthe oxidation of ammonia by oxygen has been found to be provided byzeolites which also exhibit pore size large enough to permit adequatemovement of the reactant molecules NO and NH₃ in to, and the productmolecules N₂ and H₂O out of, the pore system in the presence of sulfuroxide molecules resulting from short term sulfur poisoning and/orsulfate deposits resulting from long term sulfur poisoning. The poresystem of suitable size is interconnected in all three crystallographicdimensions. As is well known to those skilled in the zeolite art, thecrystalline structure of zeolites exhibits a complex pore structurehaving more or less regularly recurring connections, intersections andthe like. Pores having a particular characteristic, such as a givendimension diameter or cross-sectional configuration, are said to be onedimensional if those pores do not intersect with other like pores. Ifthe pores intersect only within a given plane with other like pores, thepores of that characteristics are said to be interconnected in two(crystallographic) dimensions. If the pores intersect with other likepores lying both in the same plane and in other planes, such like poresare said to be interconnected in three dimensions, i.e., to be “threedimensional”. It has been found that zeolites which are highly resistantto sulfate poisoning and provide good activity for both the SCR processand the oxidation of ammonia with oxygen, and which retain good activityeven when subject to high temperatures, hydrothermal conditions andsulfate poisons, are zeolites which have pores which exhibit a porediameter of at least about 7 Angstroms and are interconnected in threedimensions. Without wishing to be bound by any specific theory, it isbelieved that the interconnection of pores of at least 7 Angstromsdiameter in three dimensions provides for good mobility of sulfatemolecules throughout the zeolite structure, thereby permitting thesulfate molecules to be released from the catalyst to free a largenumber of the available adsorbent sites for reactant NO, and NH₃molecules and reactant NH₃ and O₂ molecules. Any zeolites meeting theforegoing criteria are suitable for use in the practice of the presentinvention; specific zeolites which meet these criteria are USY, Beta andZSM-20. Other zeolites may also satisfy the aforementioned criteria.

[0032] The above-described zeolite catalysts have been very effectivefor the selective catalytic reduction of NO_(x) with ammonia. Inparticular, an iron-promoted zeolite beta has been found most useful inthe SCR process for removing NO_(x) from gas turbine exhaust streams.Unfortunately, at the higher temperatures, e.g. 500° C. or more,provided by recent gas turbine technology, it has been found that thehydrothermal stability of such catalyst is reduced as manifest by areduced catalytic activity over time. Thus, the present invention isdirected to improving the stability of catalysts described in U.S. Pat.No. 4,961,917 for use in SCR processing. Importantly, a furtherdiscovery has been made which is believed to be relevant to all zeolitecatalysts. A novel zeolite structure has been found which is moreresistant to dealumination such as under oxidizing or hydrothermalconditions and the like. Thus, while the treatment of zeolite beta toimprove stability is a preferred embodiment of the invention inasmuch assuch zeolite catalyst has been proven to be effective in the SCRprocess, the present invention is also directed to the improvement instability under oxidizing and/or hydrothermal conditions for any zeolitecatalyst. The improvement in stability is provided by incorporatingnon-framework aluminum oxide units into a zeolite catalyst. Thenon-framework aluminum oxide units should be present in amounts of atleast 10 wt. % relative to total aluminum oxide content in the zeoliteto provide the desired stability. Accordingly, examples of zeolitecatalysts which can be is treated in accordance with this inventioninclude but are not so limited to ZSM-5, ZSM-8, ZSM-11, ZSM-12, zeoliteX, zeolite Y, beta, mordenite, erionite.

[0033] The stabilized aluminosilicate zeolites of this invention formed,for example, by the processes as described below, are believed to becharacterized as containing non-framework aluminum oxide chains whichare attached or otherwise associated with the aluminosilicate frameworkof the zeolite. FIG. 1 schematically illustrates what is believed to bethe structure of the stabilized zeolites containing the aluminosilicatezeolite framework which has attached thereto an aluminum oxide chain 10comprising alternating aluminum and oxygen atoms. Each end of thealuminum oxide chain 10 is shown as linked to the aluminosilicateframework of the zeolite. It is possible that a portion of the aluminumoxide chains formed may have only one end linked to the zeoliteframework and still provide improved stability. This structure, which isillustrated is only theorized and as such, the invention is not to bestrictly limited to the structure shown in FIG. 1. It is believed,however, that at least 10% of the aluminum oxide present in the zeoliteshould be present in the non-framework aluminum oxide units to providethe noticeable improvements in resistance to dealumination duringcatalyst use. As a consequence of the improved resistance todealumination, metal promoters such as iron (Fe²⁺) as shown in FIG. 1remain coordinated to the aluminosilicate tetrahedra of the zeoliteframework even upon use under harsh hydrothermal conditions.

[0034] Regardless of the exact association of the aluminum oxide chainto the zeolite framework, the non-framework aluminum oxide chains havebeen found to have a characteristic FT-IR adsorption peak at 3781±2cm⁻¹. This characteristic peak 12 is shown in FIG. 2 for zeolite beta,which has either been pre-steamed or which has been exchanged withcerium under acidic conditions. The FT-IR absorption band at 3781 cm⁻¹is a characteristic of non-framework aluminum in the zeolite beta, butis not present in FT-IR of untreated or dealuminized zeolite beta,(ZNX)see FIG. 2. Moreover, a zeolite beta which has been pretreated byexchange with aluminum cations or by the incorporation of aluminum oxidesuch as by slurry into the pores of the zeolite also do not show thecharacteristic absorption FT-IR band which is believed to representextra framework aluminum oxide units linked to or otherwise associatedwith the aluminosilicate framework found with the stabilized zeolites ofthis invention. Importantly, to provide the enhanced stability of thisinvention, the FT-IR peak at 3781 cm⁻¹ should have a peak area of atleast 0.05 absorbance unit×cm⁻¹, preferably at least 0.1 absorbanceunit×cm⁻¹, and, most preferably, at least 0.2 absorbance unit×cm⁻¹.

[0035] The improved stability provided to aluminosilicate zeolites hasso far been achieved by two distinct processes. In the first process,the zeolite is presteamed under specific conditions prior to theinclusion of the metal promoters. The zeolite to be presteamed can be inthe hydrogen, ammonium, or metal cationic form other than the sodiumform. It has been found that the sodium form (Na⁺) of the zeolite willnot form the non-framework aluminum oxide by either of the treatments ofthis invention. The steaming conditions are such as to provide improvedresistance to dealumination during use under high temperature, oxidizingconditions, and harsh hydrothermal environments. It is believed-that thesteaming conditions are such as to provide the non-framework aluminumoxide chains and are not such as to merely dealuminate the zeolite so asto increase the silica to alumina ratio.

[0036] In accordance with this invention, zeolite beta can be providedwith improved stability for catalyzing the selective catalytic reductionof NO_(x) with ammonia by pre-steaming the catalyst at temperatures ofgreater than 600° C. to 800° C. for a period of time of 0.25 to 8 hours.The preferred steam temperature is 650° C. to 750° C. The length of thepre-steaming treatment is preferably from 0.5 to 4 hours and mostpreferably from 1 to 2 hours. The temperatures for the steamingtreatment of this invention are generally lower than those used forremoving aluminum from the framework of zeolites, and the length oftreatment is generally shorter than that usually provided fordealumination of the zeolite framework. Steaming conditions used toprovide stability for other aluminosilicate zeolites other than zeolitebeta should be similar to the conditions set forth. Such conditions canbe readily determined by steaming the zeolite at conditions such as toprovide the peak at 3781±2 cm⁻¹ and peak area observed by FT-IR asdiscussed above.

[0037] Subsequent to the steaming treatment, the zeolite can be promotedwith various metals. For the use of zeolite beta as in the selectivecatalytic reduction of NO_(x) with ammonia, the pre-steamed zeolite betacan be promoted with iron and copper as described in U.S. Pat. No.4,961,917, the entire contents of which are herein incorporated byreference. In general, the iron or copper promoter, iron beingpreferred, is added in amounts of from about 0.1 to 30% by wt.calculated as metal based on the total weight of the metal and thezeolite. Preferred levels of the iron promoter ranges from 0.5 to 2.5wt. %, and most preferred from about 0.7 to 1.5 wt. %.

[0038] The second method which has been found to provide zeolite betawith hydrothermal stability during the selective catalytic reduction ofNO_(x) with ammonia is to pre-treat the zeolite beta with a compound ofthe lanthanide series, such as cerium, prior to exchange with thepromoter metal such as iron. Again, it is theorized that the lanthanidebeing slightly acidic results in the scission of the aluminum oxide fromthe zeolite framework which aluminum oxide is then recombined asaluminum oxide chains, which are linked to or associated with thezeolite framework. The lanthanides such as cerium are not so acidic asto cause the complete dealumination and removal of the aluminum oxidefrom the zeolite. In the lanthanide exchange, an aqueous solution of alanthanide salt at a pH of 2 to 4 is first exchanged into a hydrogen orammonium zeolite beta to provide a level of lanthanide of approximately0.25 to 1 wt. % on the zeolite. A metal cationic form other than sodiumcan also be treated with the lanthanide salt. Subsequent exchange withthe metal promoter such as iron is achieved by conventional methods byuse of an aqueous metal salt to provide the level of metal promoter asdescribed above. Again, although improved stability has been found withzeolite beta when used to catalyze the selective catalytic reduction ofNO_(x) with ammonia, it is believed that stability for other zeolitecatalysts can be achieved inasmuch as the treatment with the lanthanidesuch as cerium provides the non-framework aluminum oxide chains andconsequent increased resistance to dealumination under high temperature,oxidizing or hydrothermal environments;

EXAMPLE 1

[0039] Preparation of a standard iron-promoted zeolite beta catalyst wasas follows:

[0040] 1. To 1,000 g of DI water (heated to 80° C.) was added 25.5 g ofFeSO₄.7H₂O.

[0041] 2. To this solution was added 212.5 g of Na+Beta.

[0042] 3. The slurry in step 2 was kept with continued stirring at 80°C. for 1 hour and then filtered through a filter press and washed withan additional 2,000 g of water.

EXAMPLE 2

[0043] Preparation of honeycomb catalyst.

[0044] The filter cake formed in step 3 of Example 1 was slurried in 80g of water. To this mixture, 44.3% of 20% Zirconium acetate solution wasadded. A defoamer (5 drops of NAPCO NXZ, defoamer by Hankel Corp.) wasalso added to the mixture and the whole slurry was sheared with a highshear mixer so as to provide a particle size distribution wherein 90% ofthe particles were less than 20 microns.

[0045] A honeycomb substrate was then dipped coated with this mixture,dried and calcined to 400° C.

EXAMPLE 3

[0046] Preparation of a stabilized iron-promoted zeolite beta was asfollows:

[0047] 1. The material prepared in Example 1 was spray dried and thencalcined at 650° C. in the presence of 10% steam for 2 hours.

[0048] 2. This material (212.5 g) was then added to an iron sulfatesolution as described in Example 4 below. Concentrated sulfuric acid wasthen added to maintain a pH 2.

[0049] 3. The resulting solution was then stirred for 1 hour, filteredand washed with 2,000 g of DI water.

[0050] 4. A-honeycomb catalyst was then prepared via the process asdescribed in Example 2 above.

EXAMPLE 4

[0051] The iron sulfate solution used in Example 3 above was prepared asfollows:

[0052] 25.5 g of FeSO₄.7H₂O were completely dissolved in 1000 g of DIwater. Concentrated sulfuric acid was added slowly to the solution toobtain a pH of 2.

EXAMPLE 5

[0053] A NH₄+beta was promoted with cerium/iron as follows:

[0054] 1. 100 g of NH₄+beta were dispersed in one liter of 0.05 molarcerium nitrate solution and stirred for 24 hours, filtered and thenwashed with 2,000 ml. of DI water.

[0055] 2. This filter cake was added to 1 liter of 0.05 molar FeCl₂solution, stirred 24 hours, dried and then washed with 2,000 ml of DIwater.

[0056] 3. This dry filter cake was then calcined at 600° C. for 6 hours.The final product contained about 0.7% CeO₂and 1.4% Fe₂O₃.

[0057] 4. A honeycomb catalyst was then prepared via the process asdescribed in Example 2.

EXAMPLE 6

[0058] A sodium zeolite beta was promoted with Aluminum/iron as follows:

[0059] 1. 200 g of Na+beta was dispersed in 1 liter of 1 molar aluminumnitrate solution, stirred for 5 hours, filtered and then washed with2,000 ml. of DI water. The mixture was then dried and calcined at 550°C. for 2 hours.

[0060] This powder was then added to an iron sulfate solution preparedvia Example 4. The pH of the mixture was adjusted to pH 2, stirred for 1hour, filtered and then washed with 2,000 ml of water.

[0061] A honeycomb catalyst was prepared with this material via Example2.

EXAMPLE 7

[0062] The zeolite beta catalysts of Examples 1, 3, 5 and 6 were testedfor activity relative to conversion of NO_(x) as described below.

[0063] Activity

[0064] The performance of each of the above catalysts was evaluated witha flow thru reactor at 30,000 space velocity with 200 ppm NOx and 200ppm NH₃. The activity was tested at 425° C. and 550° C. Activity wasmeasured as % conversion of NO_(x) for the fresh catalyst and catalystaged at 650° C., 30% steam for 387 hours. Table 1 provides datagenerated at 425° C. and Table 2 provides data generated at 550° C.TABLE 1 Fresh Aged Activity Activity Example 3 Stabilized iron beta 9258 Example 5 Cerium/iron beta 90 57 Example 6 Alumina/iron beta 92 48Example 2 Iron beta 91 42

[0065] TABLE 2 Fresh Aged Activity Activity Example 3 Stabilized ironbeta 92 61 Example 5 Cerium/iron beta 92 57 Example 6 Alumina/iron beta92 47 Example 2 Iron beta 91 44

[0066] It can be seen that the conversion of NO_(x) using the agedstabilized catalysts of this invention is improved relative to the othercatalysts.

[0067] Further data is provided in FIGS. 3 and 4 which show theimprovement in catalyst stability (found via improved NO_(x) conversion)using stabilized iron-promoted zeolite beta catalysts of this invention,steamed at 650° C. and 700° C., respectively, for 2 hours and Ceriumexchanged beta compared with untreated beta (ZNX). FIG. 3 shows resultsof NO_(x) conversion at 430° C., while FIG. 4 shows results of NO_(x)conversion at 550° C.

[0068] Once given the above disclosure, many other features,modifications, and improvements will become apparent to the skilledartisan. Such other features, modifications, and improvements are,therefore, considered to be a part of this invention, the scope of whichis to be determined by the following claims.

We claim:
 1. A metal-promoted aluminosilicate zeolite having improvedstability formed by presteaming an aluminosilicate zeolite at atemperature of 600° C.-800° C. for a period of time of 0.25 to 8 hours,said presteaming not providing significant dealumination of saidaluminosilicate zeolite, subsequently adding metal to said presteamedzeolite.
 2. The stabilized aluminosilicate zeolite of claim 1, whereinsaid metal is iron.
 3. The stabilized aluminosilicate zeolite of claim1, wherein said metal is added in amounts of from 0.1 to 30% by weightcalculated as metal based on the total weight of the metal andaluminosilicate zeolite.
 4. The stabilized aluminosilicate zeolite ofclaim 3, wherein said metal is added in amounts of from 0.5 to 2.5weight percent based on the total weight of the metal and the zeolite.5. The stabilized aluminosilicate zeolite of claim 4, wherein said metalis iron which is present in amounts of 0.7 to 1.5 weight percent as ironbased on the total weight of iron and the zeolite.
 6. The stabilizedaluminosilicate zeolite of claim 1, wherein said zeolite has a silica toalumina ratio of at least about 8, and a pore structure which isinterconnected in all three crystallographic dimensions by pores havingan average kinetic pore diameter of at least about 7 Δ.
 7. Thestabilized aluminosilicate zeolite of claim 6 comprising zeolite beta.8. A stable, metal-promoted aluminosilicate zeolite prepared bycontacting an aluminosilicate zeolite with a lanthinide salt byion-exchange and subsequent to contact with said lanthinide salt, addinga metal promoter by ion-exchange to said lanthinide-treatedaluminosilicate zeolite.
 9. The stabilized aluminosilicate zeolite ofclaim 8, wherein said lanthinide salt is a cerium salt.
 10. Thestabilized aluminosilicate zeolite of claim 8, wherein said metalpromoter is iron.
 11. The stabilized aluminosilicate zeolite of claim 8,wherein said metal promoter is added in amounts of from 0.1 to 30% byweight calculated as metal based on the total weight of the metal andzeolite.
 12. The aluminosilicate zeolite of claim 10, wherein said ironis added in amounts of from about 0.5 to 2.5 weight percent.
 13. Thestabilized aluminosilicate zeolite of claim 12, wherein said zeolite iszeolite beta.
 14. The stabilized aluminosilicate zeolite of claim 8,wherein said zeolite has a silica to alumina ratio of at least about 8,and a pore structure which is interconnected in all threecrystallographic dimensions by pores having an average kinetic porediameter of at least about 7 Δ.
 15. The stabilized aluminosilicatezeolite of claim 14, wherein said metal promoter is iron which is addedin amounts of from 0.5 to 2.5 weight percent as metal based on the totalweight of the metal and the zeolite.
 16. A stabilized aluminosilicatezeolite containing alternating aluminum and oxygen atoms separate fromthe framework of said zeolite, said non-framework alternating aluminumand oxygen atoms comprising at least 10 wt. % of total aluminum oxide insaid zeolite.
 17. The stabilized aluminosilicate zeolite of claim 16,comprising said non-framework alternating aluminum and oxygen atoms inthe form of a plurality of chains.
 18. The stabilized aluminosilicatezeolite of claim 16, wherein said zeolite includes a metal promoter. 19.The stabilized aluminosilicate zeolite of claim 18, wherein said metalpromoter is ion-exchanged into said zeolite.
 20. The stabilizedaluminosilicate zeolite of claim 19, wherein said metal promoter is ironand said zeolite is zeolite beta.
 21. The stabilized aluminosilicatezeolite of claim 20, wherein said iron is present in amounts of 0.1 to30 weight percent by weight calculated as metal and based on the totalweight of the metal and the zeolite.
 22. The stabilized aluminosilicatezeolite of claim 21, wherein said iron is present in amounts of 0.5 to2.5 weight percent based on metal.
 23. The stabilized aluminosilicatezeolite of claim 21, wherein said iron is present in the amounts of 0.7to 1.5 weight percent based on iron.
 24. The stabilized aluminosilicatezeolite of claim 16, wherein said zeolite has a silica to alumina ratioof at least about 8, and a pore structure which is interconnected in allthree crystallographic dimensions by pores having an average kineticdiameter of at least about 7 Δ.
 25. The stabilized aluminosilicatezeolite of claim 24, further including a metal promoter.
 26. Astabilized metal-promoted aluminosilicate zeolite having an FT-IRabsorption peak at 3781±2 cm⁻¹.
 27. The stabilized aluminosilicatezeolite of claim 26, wherein said zeolite has a silica to alumina ratioof at least about 8, and a pore structure which is interconnected in allthree crystallographic dimensions by pores having an average kineticpore diameter of at least about 7 Δ.
 28. The stabilized aluminosilicatezeolite of claim 27, wherein said zeolite is selected from the groupconsisting of ultrastable Y, beta and ZSM-20.
 29. The stabilizedaluminosilicate zeolite of claim 26 selected from the group consistingof ZSM-5, ZSM-8, ZSM-11, ZSM-12, zeolite X, zeolite Y, beta, mordeniteand erionite.
 30. The stabilized aluminosilicate zeolite of claim 26,wherein said zeolite is zeolite beta.
 31. The stabilized aluminosilicatezeolite of claim 26, wherein said metal promoter is present in amountsof 0.1 to 30 percent by weight calculated as metal and based on thetotal weight of the metal and the zeolite.
 32. The stabilizedaluminosilicate zeolite of claim 26, wherein said zeolite is zeolitebeta and said metal promoter is iron.
 33. The stabilized aluminosilicatezeolite of claim 32, wherein said iron is present in amounts of from 0.5to 2.5 weight percent.
 34. The stabilized aluminosilicate zeolite ofclaim 33, wherein said iron is present in amounts of from 0.7 to 1.5weight percent.
 35. A stabilized aluminosilicate zeolite catalystcharacterized by FT-IR absorption peak at 3781±2 cm⁻¹ and wherein saidpeak has an area of at least 0.05 absorbance unit×cm⁻¹.
 36. Thestabilized aluminosilicate zeolite of claim 35, wherein said zeolite hasa silica to alumina mole ratio of at least about 8, and a pore structurewhich is interconnected in all three crystallographic dimensions bypores having an average kinetic pore diameter of at least about 7 Δ. 37.The stabilized aluminosilicate zeolite of claim 36, wherein said zeoliteis selected from the group consisting of ultrastable Y, beta and ZSM-20.38. The stabilized aluminosilicate zeolite of claim 36, wherein saidzeolite is zeolite beta.
 39. The stabilized aluminosilicate zeolite ofclaim 35, which is ion-exchanged with a metal.
 40. The stabilizedaluminosilicate zeolite of claim 39, wherein said metal comprises 0.1 to30 weight percent by weight calculated as the metal and based on thetotal weight of the metal and the zeolite.
 41. The stabilizedaluminosilicate zeolite of claim 40, wherein said zeolite is beta andsaid metal is iron.
 42. A process for improving the stability of analuminosilicate zeolite catalyst under oxidizing and/or hydrothermalconditions, comprising treating said aluminosilicate zeolite with steamat a temperature of 600° C. to 800° C. for a period of time of 0.25 to 8hours without substantially dealuminizing said zeolite.
 43. The processof claim 42, wherein the temperature of said steam is 650° C. to 750° C.and the length of treatment is from 0.5 to 4 hours.
 44. The process ofclaim 43, wherein the length of the steam treatment is from 1 to 2hours.
 45. The process of claim 42, wherein said zeolite has a silica toalumina mole ratio of at least about 8, and a pore structure which isinterconnected in all three crystallographic dimensions by pores havingan average kinetic pore diameter of at least about 7 Δ.
 46. The processof claim 45, wherein said zeolite is selected from the group consistingof ultrastable Y, beta and ZSM-20.
 47. The process of claim 46, whereinsaid zeolite is zeolite beta.
 48. The process of claim 42, wherein saidzeolite is selected from the group consisting of ZSM-5, ZSM-8, ZSM-11,ZSM-12, X, Y, beta, mordenite, and erionite.
 49. The process of claim 42comprising adding a metal promoter to said steam-treated zeolite. 50.The process of claim 49, wherein said metal promoter is present in theamounts of 0.1 to 30 percent by weight calculated as metal and based ona total weight of the metal and the zeolite.
 51. The process of claim50, wherein said zeolite is zeolite beta and said metal promoter isiron.
 52. The process of claim 49, wherein said metal promoter is addedby ion-exchanging said steam-treated zeolite with a metal salt.
 53. Aprocess for stabilizing an aluminosilicate zeolite catalyst for useunder oxidizing and/or hydrothermal conditions comprising ion exchangingsaid aluminosilicate zeolite with a lanthinide salt under acidicconditions insufficient to substantially dealuminate said zeolite and toprovide a level of lanthinide of approximately 0.25 to 1 weight percentbased on lanthinide on said zeolite.
 54. The process of claim 53,wherein said lanthinide salt is-a cerium salt.
 55. The process of claim53, wherein said zeolite has a silica to alumina mole ratio of at leastabout 8, and a pore structure which is interconnected in all threecrystallographic dimensions by pores having an average kinetic porediameter of at least about 7 Δ.
 56. The process of claim 55, whereinsaid zeolite is selected from the group consisting of ultrastable Y,beta and ZSM-20.
 57. The process of claim 53, wherein said zeolite isselected from the group consisting of ZSM-5, ZSM-8, ZSM-11, ZSM-12, X,Y, beta, mordenite and erionite.
 58. The process of claim 53, whereinsubsequent to ion exchange with said lanthinide salt, said treatedzeolite is ion exchanged with a catalytic metal salt to add saidcatalytic metal to said zeolite by ion-exchange.
 59. The process ofclaim 58, wherein said catalytic metal salt is an iron salt.
 60. Theprocess of claim 59, wherein said zeolite is zeolite beta and said ironis added to said zeolite in amounts from 0.1 to 30 percent by weightcalculated as iron.
 61. The process of claim 60, wherein said lanthinidesalt is a cerium salt.
 62. The process of claim 6,1, wherein the iron ispresent in amounts of 0.5 to 2.5 weight percent as metal on saidzeolite.
 63. The process of claim 62, wherein said iron is present inamounts of from about 0.7 to 1.5 weight percent as iron on said zeolite.64. A method for the reduction of nitrogen oxides with ammonia, whichcomprises: contacting a gaseous stream containing nitrogen oxides andammonia at a temperature of from about 250° C. to 600° C. with acatalyst composition comprising: a metal-promoted aluminosilicatezeolite having improved stability formed by presteaming analuminosilicate zeolite at a temperature of 600° C.-800° C. for a periodof time of 0.25 to 8 hours, said presteaming not providing significantdealumination of said aluminosilicate zeolite, adding metal to saidpresteamed zeolite, said zeolite having a silica to alumina mole ratioof at least about 8, and a pore structure which is interconnected in allthree crystallographic dimensions by pores having an average kineticpore diameter of at least about 7 Δ.
 65. The method of claim-64, whereinsaid metal is added in amounts of from 0.1 to 30% by weight calculatedas metal based on the total weight of the metal and aluminosilicatezeolite.
 66. The method of claim 65, wherein the metal promoter ispresent in the amount of from about 0.5 to 2.5 percent by weight of thetotal weight of the catalytic material.
 67. The method of claim 66,wherein the promoter comprises iron.
 68. The method of claim 64, whereinthe zeolite is selected from the group consisting of USY, beta andZSM-20.
 69. The method of claim 67, wherein the zeolite is beta.
 70. Themethod of claim 64, wherein the catalyst composition further includes arefractory binder admixed with the zeolite.
 71. A method for thereduction of nitrogen oxides with ammonia, which comprises: contacting agaseous stream containing nitrogen oxides and ammonia at a temperatureof from about 250° C. to 600° C. with a catalyst composition comprising:a stable, metal-promoted aluminosilicate zeolite prepared by ionexchanging an aluminosilicate zeolite with a lanthinide salt andsubsequent to said ion exchange with said lanthinide salt, adding ametal promoter by ion-exchange to said lanthinide ion exchangedaluminosilicate zeolite, said zeolite having a silica to alumina moleratio of at least about 8, and a pore structure which is interconnectedin all three crystallographic dimensions by pores having an averagekinetic pore diameter of at least about 7 Δ.
 72. The method of claim 71,wherein said metal is added in amounts of from 0.1 to 30% by weightcalculated as metal based on the total weight of the metal andaluminosilicate zeolite.
 73. The method of claim 72, wherein the metalpromoter is present in the amount of from about 0.5 to 2.5 percent byweight of the total weight of the catalytic material.
 74. The method ofclaim 73, wherein the promoter comprises iron.
 75. The method of claim71, wherein the zeolite is selected from the group consisting of USY,beta and ZSM-20.
 76. The method of claim 75, wherein the zeolite isbeta.
 77. The method of claim 71, wherein the catalyst compositionfurther includes a refractory binder admixed with the zeolite.
 78. Amethod for the reduction of nitrogen oxides with ammonia, whichcomprises: contacting a gaseous stream containing nitrogen oxides andammonia at a temperature of from about 250° C. to 600° C. with acatalyst composition comprising: (a) a stabilized aluminosilicatezeolite comprising non-framework chains of alternating aluminum andoxygen atoms separate from the framework of the zeolite, at least 10% ofthe aluminum oxide of said zeolite, being in the form of saidnon-framework chain, said zeolite having a silica to alumina mole ratioof at least about 8, and a pore structure which is interconnected in allthree crystallographic dimensions by pores having an average kineticpore diameter of at least about 7 Δ.; and (b) a metal promoter.
 79. Themethod of claim 78, wherein said metal is added in amounts of from 0.1to 30% by weight calculated as metal based on the total weight of themetal and aluminosilicate zeolite.
 80. The method of claim 79, whereinthe metal promoter is present in the amount of from about 0.5 to 2.5percent by weight of the total weight of the catalytic material.
 81. Themethod of claim 80, wherein the promoter comprises iron.
 82. The methodof claim 78, wherein the zeolite is selected from the group consistingof USY, beta and ZSM-20.
 83. The method of claim 82, wherein the zeoliteis beta.
 84. The method of claim 78, wherein the catalyst compositionfurther includes a refractory binder admixed with the zeolite.
 85. Amethod for the reduction of nitrogen oxides with ammonia, whichcomprises: contacting a gaseous stream containing nitrogen oxides andammonia at a temperature of from about 250° C. to 600° C. with acatalyst composition comprising: a stabilized metal-promotedaluminosilicate zeolite having an FT-IR adsorption peak at 3781±2 cm⁻¹.86. The method of claim 85, wherein said metal is added in amounts offrom 0.1 to 30% by weight calculated as metal based on the total weightof the metal and aluminosilicate zeolite.
 87. The method of claim 86,wherein the metal promoter is present in the amount of from about 0.5 to2.5 percent by weight of the total weight of the catalytic material. 88.The method of claim 87, wherein the promoter comprises iron.
 89. Themethod of claim 85, wherein the zeolite is selected from the groupconsisting of USY, beta and ZSM-20.
 90. The method of claim 89, whereinthe zeolite is beta.
 91. The method of claim 85, wherein the catalystcomposition further includes a refractory binder admixed with thezeolite.
 92. The method of claim 64, wherein said gaseous stream iscontacted with said catalyst at a temperature of greater than 500° C.93. The method of claim 71, wherein said gaseous stream is contactedwith said catalyst at a temperature of greater than 500° C.
 94. Themethod of claim 78, wherein said gaseous stream is contacted with saidcatalyst at a temperature of greater than 500° C.
 95. The method ofclaim 85, wherein said gaseous stream is contacted with said catalyst ata temperature of greater than 500° C.
 96. The stabilized aluminosilicatezeolite catalyst of claim 35, wherein said peak has an area of at least0.1 absorbance unit×cm⁻¹.
 97. The stabilized aluminosilicate zeolitecatalyst of claim 35, wherein said peak has an area of at least 0.2absorbance unit×cm⁻¹.
 98. The method of claim 85, wherein said peak asan area of at least 0.05 absorbance unit×cm⁻¹.
 99. The method of claim85, wherein said peak as an area of at least 0.1 absorbance unit×cm⁻¹.100. The method of claim 85, wherein said peak as an area of at least0.2 absorbance unit×cm⁻¹.